Sedums, also known as stonecrops, are perennial plants that have star-shaped blooms during the summer months. There are several varieties available, including sedums that grow only a couple inches in height, and others that reach more than 2 feet. While you don't need to deadhead or pinch back sedum flowers after they have bloomed (they actually add interest to the garden as they seed), you do need to prune your sedums at least once a year to get rid of the past season's dead growth.
Sterilize your pruning shears or loppers prior to pruning your sedums. While it's not necessary to sterilize your tools between each use, if you used the tools with diseased plants, it is a must. One easy method to sterilize tools is to wet a thick cotton rag with rubbing alcohol and carefully wipe down the blades. Dry with a clean cloth.
Prune the plants back to about 1-2 inches above the ground after the first killing frost in the fall. If you miss this occasion, you still have until early spring before new growth appears to prune your sedums.
Cut off about one-third to one-half of your sedums' height when tall varieties begin to get lanky, usually between May and July, depending on your climate. This step is optional, but will encourage more compact plants. Note, however, that your sedums will not bloom for several weeks after this pruning.